Today we'll be
talking about the least common ground-based non-precision approach, the
NDB approach. As the name implies, NDB approaches are approach procedures
which use NDBs as the primary navigational aid. Like VORs, NDBs can be
located either on the airport or at a remote location. Approach procedures
can be based on either. NDBs are very old and and their operation is very
simple, yet flying them precisely is difficult. You will notice that
approach minimums for NDB approaches are higher than those for a VOR or
other. This is because NDB signals are less precise and they are subject
to several types of interference. I won't discuss the use of the ADF in
this lesson, so if you're not familiar with it's use, you may want to skip
this lesson for now. The key to remember is that ADF needle always points
to the station. One other thing to remember is that we don't
get DME information from the NDB, so we have to be more aware of our
position. So, now that we know a bit about NDB approach, let's brief our
chart and then go flying...

Since we've already gone over
chart symbology, I'll just touch lightly on most of these things. "A"
tells us that we're going to be doing the NDB (or GPS) Rwy 11R approach at
Vero Beach. Because the approach is categorized with a runway number(11R),
we know that the final approach segment of this approach will bring us to
within 30 degrees of the extended centerline of 11R. We also see that the
primary navaid is the Vero Beach NDB (VEP), it's frequency being 392. "B"
points to VEP and we see above the ID box that this is the Initial
Approach Fix (IAF). There are no other IAFs for this approach. "C" shows
us our outbound bearing of 265 degrees. "D" shows us our procedure turn,
the course reversal we will fly to establish ourselves on course. "E"
indicates our MAP. We see that the MAP is located at the NDB. "F" shows
us our minimums, 760ft MSL/1 mile vis. for both straight-in and
circle-to-land.

Something you'll notice about this approach is the absence
of a Final Approach Fix (FAF). Because we simply make our procedure turn
and then descend to our MDA, the beginning of the Final Approach segment
will depend on how far out we make our procedure turn. In this case, we
have what is called a Final Approach Point (FAP) which is wherever you
complete the procedure turn. "G" shows us our time to the Missed Approach
Point (MAP), which in our case, isn't applicable. It simply says that the
MAP is at the NDB. So, we don't need time to find our MAP, we will know
because we'll pass over the NDB and then ADF needle will flip. OK, now
that we've briefed our plate, let's do this...

Today's
weather is ceiling 850ft overcast, visibility 3 miles. We'll be practicing
with no wind because wind makes NDB procedures really tough. We'll be
doing the full procedure, starting at VEP. So, what we're going to do is
take off from Vero Beach, climbing to 3000ft, and request the full NDB 11R
approach. At that point, Center will say "9246F proceed direct to the
beacon, cleared full NDB 11R approach, contact tower 126.3 when procedure
turn inbound". So, now we've tuned in VEP and turned so the head of the
needle is pointing to 0 so we know we're headed directly to the NDB. We're
level at 3000ft and proceeding to the NDB. We see that our outbound
bearing for the initial approach segment is 265 degrees. So, as we pass
over the NDB, we will turn to a heading of approximately 265 degrees,
looking for the head of the needle to swing around so the tail is now
pointing to 0. We're now actually on the approach, proceeding outbound.

Since we don't have DME to give us our distance from the NDB, we will
start our timer so that we have an idea of how far out we are. Since we're
going 90kts, it will take us about 6.5 minutes to go 10NM from the NDB.
Another trick that we use in this particular case is to reference the DME
readout from the VRB VOR. Since we know from yesterday's procedure that
the VOR is 3.5DME from the MAP. Add another 0.5NM since the NDB is in the
middle of the field and we've can say that we don't want to go out any
further than about 6DME from the VOR and that should keep us within 10NM
of the NDB. This is a very general backup and you wouldn't depend on it
entirely, but it can be helpful. In the profile view, we see that we can
also descend to 2000ft until the completion of the procedure turn. So,
we'll start a descent to 2000ft.

Figure 1: On the procedure outbound from the NDB. Heading 265 and descending to
2000 feet.

This is position "1" marked on the chart above and the map-view below.

I'm going
out about 3 minutes from the NDB before I start my turn. You can see at
"D" that the first turn is to a heading of 310 degrees. This is a
heading, NOT a radial from a VOR. So, when the timer says 3 minutes, I'll
make a turn to 310 degrees and start my timer again. We want to fly the
procedure turn outbound for 1 minute. When 1 minute is up on our timer,
we'll start a 180 degree turn to a heading of 130 degrees and then fly
inbound. MAKE SURE to make standard rate turns (wings set on the turn index
line on the turn coordinator) or else the procedure turn won't work out.
At this point, we're inbound on the procedure turn, so it's time to call
the tower and report where we are. The tower will then say "9246F roger,
runway 11R cleared to land". Now, here's where it gets a bit tricky. Our
needle is going to be deflected off to the left a bit. So, how do we know
when we've intercepted our course? Well, we're now on a heading of 130
degrees and we want to fly inbound on a bearing to the NBD of 085 degrees.
That's a 045 degree difference. So, when the needle swings to the left 045
degrees from 0 (in this case it will be pointing to 315 degrees), we know
we're on course.

Figure 2: Procedure turn inbound. Level at 2000, heading of 130. Note the ADF needle.
No CDI to help us intercept the inbound course on this one.

This is position "2" on the chart and the map-view.

Now we want
to start a turn to a heading of 085. As we do this, the needle will swing
slowly so that the head should line up on 0 when we roll out on a heading
of 085 degrees. Once we're established inbound (on the inbound bearing), we
may begin our descent down to the MDA of 760ft MSL. We're now at the FAP,
so let's drop the gear. Our time to descend to the MDA is dependant on how
far we went out on the procedure turn, so we must plan our descent
accordingly to give us time at the MDA to look outside for the runway. We
don't need to start our timer since the MAP is at the NDB.

Figure 3: Inbound on the 085 heading and descending to MDA. Upon reaching MDA we watch
for the runway. MAP is the NDB, so if we don't see it by then we execute a missed approach.

Note position "3" on the chart and the map-view.

Now we're
done with communicating and configuring and all of our concentration is on
flying. We going to level off NO LOWER than 760ft MSL and proceed along
course until reaching the MAP, looking up every few seconds for the
runway. Hopefully we would get the runway in sight before reaching the
MAP. If not, we would immediately begin the missed approach upon reaching
the MAP, calling the tower to let them know we're going missed. In this
case however, we've got the runway just in sight, so we'll continue the
approach and make a normal landing.

Figure 4: At MDA, runway in sight, we continue the descent and land. Note the angle of
the approach relative to the runway. Pick up the VASI for glidepath guidance and bank right, rolling out on the runway centerline.

Note position "4" on the chart and the map-view.

You can see
that the approach course or bearing doesn't lead us directly to the runway
threshold in every case. That's another drawback of non-precision
approaches. You can also see from the overhead view that even though I
flew the course as best as I could within the precision of the instrument,
the inbound leg is not exactly lined up with the outbound leg. Such is the
inaccuracy of the NDB. Even though we get less information from it, it is
still perfectly usable and excellent practice. Have fun!

Practice
You had to ask? Depart runway 11 at Vero Beach. Fly for 4 minutes then turn left and proceed direct VEP, then fly the full procedure
starting at VEP.